Construction works of Stage 1 of the Harbour Area Treatment Scheme (HATS) commenced in 1994. This stage comprised the construction of a chemically-enhanced primary treatment (CEPT) plant at Stonecutters Island, an outfall tunnel, the comprehensive upgrading of seven preliminary treatment works and seven tunnels for collecting sewage from urban Kowloon, Tsing Yi, Kwai Chung, Tseung Kwan O and eastern Hong Kong Island and conveying it to Stonecutters Island. The tunnel system was completed in December 2001 for full commissioning of HATS Stage 1.
Following the full commissioning of Stage 1 in December 2001, around 75% of the sewage generated in the harbour area is now treated at the Stonecutters Island Sewage Treatment Works (SCISTW) and discharged through the outfall to the western harbour area.
HATS Stage 1 has on average increased dissolved oxygen in the harbour waters by about 10%. In addition, the levels of key pollutants in the harbour area waters have generally decreased:
- Unionised Ammonia (UIA) has reduced by 31%;
- Nutrients, in terms of total inorganic nitrogen (TIN) and Orthophosphate (which in rich supply can increase the likelihood of red tides), have reduced by 16% and 36%; and
- The overall E.coli level, which is an indicator of disease-causing microorganisms, has reduced by some 50%.
The following achievements and events were significant in the development of HATS Stage 1.
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